Propagate UTF-8 flag during Rope operations

[Girgias]

Forgot to handle this concatenation case.

[nielsdos]

The propagation code for the VM looks good, but you also might need to update the JIT, in particular I think you need to update zend_jit_rope_end() in zend_jit_helpers.c.

[Girgias]

The propagation code for the VM looks good, but you also might need to update the JIT, in particular I think you need to update zend_jit_rope_end() in zend_jit_helpers.c.

Ah yes, that looks like it needs to!

[iluuu1994]

LGTM

[iluuu1994]

@Girgias I guess it makes sense to wait for Dmitry's response to see whether the VM overhead is ok.

[Girgias]

@Girgias I guess it makes sense to wait for Dmitry's response to see whether the VM overhead is ok.

This is kinda a follow-up on #10463 and #10490, so the VM overhead has already been added. But in any case propagating this flags allows to not need to check certain strings are UTF-8 while using ext/mbstring, and probably could find more use cases elsewhere.